Evaluation of Clinical Equivalence Between Two Lubiprostone Products

Main Inclusion Criteria:

• 1. Male or non-pregnant females aged 18 and older with a clinical diagnosis of chronic idiopathic constipation defined as, on average, < 3 spontaneous bowel movements (SBMs) per week for the past 6 months and confirmed by daily diary during the 14 day baseline lead-in period. An SBM is defined as any bowel movement that did not occur within 24 hours after rescue medication use.
• Have 1 or more of the following symptoms related to bowel movements for at least 6 months before the baseline visit and confirmed by daily diary during the 14 Day baseline period:

• very hard (little balls) and/or hard stools for at least 25 percent of the bowel movements
• sensation of incomplete evacuation following at least 25 percent of the bowel movements
• straining at defecation at least a quarter of the time
• Women of child-bearing potential must have a negative pregnancy test prior to beginning therapy and agree to use effective contraceptive methods during the study.
• For patients aged < 50 years, documentation of the results of either a flexible sigmoidoscopy or colonoscopy performed within the 5 years prior to dosing, showing no mechanical bowel obstruction or organic disorders of the large Bowel.
• For patients aged >/= 50 years, documentation of the results of either a barium enema with flexible sigmoidoscopy or colonoscopy performed within 1 year prior to dosing, showing no mechanical bowel obstruction or organic disorders of the large bowel.

Main Exclusion Criteria:

• Females who are Pregnant, breast feeding, or planning a pregnancy.
• Patients of any age with evidence of weight loss, anemia, or rectal bleeding AND without documentation of the results of either a flexible sigmoidoscopy or colonoscopy performed during the 6 months prior to dosing.
• Patients that have documented mechanical bowel obstruction (e.g., bowel obstruction due to tumor, hernia), megacolon/megarectum, or diagnosis of pseudo-obstruction.
• Any known or suspected organic disorders of the large or small bowel (e.g., inflammatory bowel disease, ulcerative colitis, Crohn's Disease) or constipation secondary to a documented cause (e.g., surgery, bowel resection)or acute hernia.
• History of bowel resection.
• Patients who are regularly using medications know to cause constipation (narcotics, calcium channel blockers, tricyclic antidepressants).
• Hospitalized for any gastrointestinal or abdominal surgical procedure during the 3 months prior to dosing.
• Clinically significant cardiovascular, liver, lung, neurologic, renal or psychiatric disorder, or clinically significant laboratory abnormalities.
• Use of a systemic antibiotic within 4 weeks prior to the Screening Visit.
• Participation in a study with any investigational medication within the past 30 days of screening for this study or previous participation in this study.